In cellular mobile radio communication systems, the mobile communication terminal, often just called “mobile terminal”, “mobile station” or “user equipment”, must monitor reception power levels at regular rates for all of the cells in the neighbourhood, and report the measured reception power levels to the respective base stations during a call, so that the cell most suitable for a high quality transmission can be determined. In call mode, cell changes are called ‘handover’, and it is the network that decides which cell to select on the basis of the measurements reported to the network by the mobile terminal. In idle mode (when there is no call), no measurement reports are sent to the base stations and the mobile terminal itself is responsible for cell re-selection, i.e. the mobile terminal determines which is the most suitable cell to ‘camp on’. These power level measurement rates are specified by the cellular network specification, for example by the 3GPP Standard. The monitoring rates may be different for different base stations. For example, the monitoring rate of the selected or serving cell base station, which currently serves the mobile station, can be different from the monitoring rates of the adjacent cell base stations. A detail description of cell re-selection based on the monitoring information is available in 3GPP TS 45.008.
Also, when the mobile station is in idle mode, meaning that it is connected to the cellular network but that there is no ongoing call, several measurements are performed every few seconds. For example, in GSM (Global System for Mobile communications) idle mode there are seven monitorings of the reception level per paging block for each base station of up to 32 neighbouring cells. The period of paging block reading could be programmed from 0.47 seconds to 2.12 seconds. Up to five measurements must be done per neighbouring cell within the limit of a maximum rate period of five seconds to obtain an average reception power level per cell. For instance, in case of ten neighbouring cells, the measurement period for all of the cells will be approximately four seconds, with a paging period of 0.47 seconds. In non-moving mode, when the mobile terminal is essentially stationary, these power levels will not vary significantly. In GPRS (General Packet Radio Service) idle mode there are sixteen monitorings per paging block, so that in this standard the monitoring rate is much higher then in GSM-systems. These monitorings are useful for re-selection of a new cell, but the measurements are superfluous when the mobile station is not moving, for example, when the user is in his office or at home. In such situations, this monitoring is effectively a waste of power consumption which significantly decreases the autonomy of the mobile station, i.e. the duration of time the mobile station can operate without having to recharge the batteries.
An attempt to reduce power consumed in the reception level measurement is disclosed in EP1 130 937 A1. In this document, it is proposed to determine the current location of a mobile station by using the measured reception power levels for localisation of the mobile terminal in the network and to determine whether the mobile station is near the centre of the serving cell. Should that be the case, the measurement and reporting of the reception power levels to the respective base stations is suspended for all adjacent base stations. A drawback of this method is that it only works when the mobile station is near the base station of the serving cell, but does not work in situations where the mobile station is stationary but located in an intermediate zone between two or three base stations.